I would also recommend that whilst using Yoast for most SEO purposes, you should also use the Google XML Sitemaps plugin by Arne Brachhold (rather than utilising Yoasts built in sitemap functionality). It offers you much more flexibility for your sitemap. For example, you can alter the change frequency of your pages/posts, with Arne's plugin, something which the Yoast plugin doesn't allow unless you play with the PHP.
